1. Field of the Invention
Example embodiments generally relate to a rotary drive device and an image forming apparatus including the rotary drive device, for example, for providing an increased reduction ratio with a compact structure.
2. Description of the Related Art
A related-art image forming apparatus including a copier, a facsimile machine, a printer, or a multifunction printer having at least one of copying, printing, scanning, and facsimile functions, typically forms a toner image on a recording medium (e.g., a recording sheet) based on image data using an electrophotographic method.
For example, a charging device charges a surface of a photoconductor. An optical writer emits a light beam onto the charged surface of the photoconductor to form an electrostatic latent image on the photoconductor according to the image data. A development device develops the electrostatic latent image with a developer (e.g., toner) to form a toner image on the photoconductor. A primary transfer roller transfers the toner image formed on the photoconductor onto an intermediate transfer belt. After a secondary transfer roller transfers the toner image carried by the intermediate transfer belt onto the recording sheet, the toner image is fixed on the recording sheet by heat and pressure applied by a fixing device. Thus, the toner image is formed on the recording sheet.
When such image forming apparatus forms a color image, the image forming apparatus may include a plurality of photoconductors arranged along the intermediate transfer belt and a plurality of primary transfer rollers opposing the plurality of photoconductors across the intermediate transfer belt. For example, the plurality of photoconductors forms cyan, magenta, yellow, and black toner images, respectively, and the plurality of primary transfer rollers transfers the cyan, magenta, yellow, and black toner images from the photoconductors onto the intermediate transfer belt so that the cyan, magenta, yellow, and black toner images are superimposed on the intermediate transfer belt.
The image forming apparatus may further include a contact-separation mechanism designed to make the photoconductors and the primary transfer rollers contact and separate from the intermediate transfer belt. For example, when the image forming apparatus forms a monochrome image, the contact-separation mechanism separates the photoconductors for forming the cyan, magenta, and yellow toner images, respectively, and the primary transfer rollers opposing the photoconductors for forming the cyan, magenta, and yellow toner images from the intermediate transfer belt. The secondary transfer roller is separated from the intermediate transfer belt when no pressure is applied to the intermediate transfer belt before and after image formation. As a result, the photoconductors, the primary transfer rollers, and the secondary transfer roller may be protected from damage, thereby increasing the working life of the image forming apparatus while improving image quality.
Such contact-separation mechanism is activated by a rotary drive device using a planetary gear mechanism including multistage gears. The planetary gear mechanism includes a gear unit including a sun gear, a plurality of planetary gears, a planetary carrier, and an output shaft. The sun gear is fixed to the planetary carrier. The plurality of planetary gears is provided around the sun gear and engages the sun gear. Thus, when the sun gear rotates, the planetary gears rotate around the sun gear at a desired speed reduction ratio. The reduced rotation output is transmitted to the output shaft and transformed into movement of the contact-separation mechanism.
However, when a radial load is directly applied to the planetary gear mechanism over a long period of time, backlash (e.g., play) between the respective gears may fluctuate in a normal line direction. Such fluctuation of the backlash in the normal line direction may increase rotational resistance between the respective gears. When the backlash becomes too great, the gears may be excessively worn and damaged.
Therefore, there is a need for a technology to provide a rotary drive device including a planetary gear mechanism in which a plurality of gears can properly engage each other in order to obtain a large reduction ratio.